1. Field of the Invention
The present invention relates to a thermal developing apparatus using a heat treatment device for carrying out a heat treatment for a thermal developing recording material to be heat treated and utilizing a dry material over which a wet process is not carried out.
2. Description of the Related Art
As an image recording apparatus for recording an image for a medical treatment such as a digital radiography system, a CT or an MR, conventionally, there has been used a wet system for carrying out photographing or recording over a silver salt photographic type photosensitive material and then performing a wet process to obtain a reproduced image.
On the other hand, recently, attention has been paid to a recording apparatus using a dry system which does not carry out a wet process. In such a recording apparatus, a film formed of a photosensitive or thermal recording material (a photosensitive thermal recording material) or a thermal developing photosensitive material (which will be hereinafter referred to as a “thermal developing recording material”) has been used. In the recording apparatus using a dry system, moreover, a laser beam is irradiated (scanned) on the thermal developing recording material to form a latent image in an exposing section and the thermal developing recording material is then caused to come in contact with heating means to carry out thermal development in a thermal developing section, and cooling is thereafter performed and the thermal developing recording material having an image formed thereon is discharged out of the apparatus.
In such a dry system, it is possible to solve a problem of a waste water process as compared with the wet process.
As a result of the investigations of such a conventional thermal developing apparatus, however, the temperature of the thermal developing section is gradually changed by an ambient temperature and the continuous process of a thermal developing recording material. Consequently, it has been found that the density of an image gradually fluctuates. More specifically, when the ambient temperature is raised, the temperature of the thermal developing section is raised. Moreover, the temperature of the thermal developing section is also raised by the continuous process of the thermal developing recording material. For this reason, the density of the image becomes higher than a predetermined density.
FIG. 2 is a chart showing the transition of a temperature versus a time at a certain point on a thermal developing recording material while thermal developing recording materials A and B enter and get out of the thermal developing section. In FIG. 2, an axis of ordinate indicates a temperature and Ts indicates a thermal developing start temperature. The thermal development is not started at a thermal developing start temperature which is less than Ts. The thermal development is started to progress at a thermal developing start temperature which is equal to or higher than Ts. An axis of abscissa indicates a time. Both A and B indicate thermal developing recording materials. The thermal developing recording material A passes through the thermal developing section in which a temperature obtained immediately after the start of an operation is not raised completely and the thermal developing recording material B passes through the thermal developing section in which the temperature is raised by a continuous operation for a long period of time. The thermal developing recording material A on which a latent image is recorded in a recording section at a former stage enters the thermal developing section through a transfer section and is thus heated, and the development progress temperature Ts is reached at a time t10 and the development progress is started. Then, the temperature of the thermal developing recording material A is raised and is maintained to be constant by a warm tone at the development progress temperature or more, and the thermal developing recording material A gets out of the thermal developing section and moves to a next cooling section. At a time t11 in the middle, the temperature reaches a temperature which is less than the development progress temperature Ts. Consequently, the thermal development progress is stopped.
In this case, a development progress time tA of the thermal developing recording material A is expressed in an equation 1.tA=t11−t10  (Equation 1)
However, when the operation of the apparatus progresses, the temperature of the thermal developing section is raised by a rise in the ambient temperature and the continuous process of the thermal developing recording material. Consequently, the thermal developing recording material B does not reach the development progress start temperature Ts at a time t20 but the time t10. Moreover, if the thermal development progress stops at the same time t11, a development progress time tB of the thermal developing recording material B is expressed in an equation 2.tB=t11−t20  (Equation 2)
As a result of comparison between the equations 1 and 2, the development progress time of the thermal developing recording material B is increased by a difference Δt of tB−tA. Accordingly, the density of an image is increased correspondingly.
Furthermore, the conventional printer of this type has a mechanism requiring heat-up. Accordingly, a print process is not executed until predetermined heat-up is completed. On the other hand, a printer is to be used urgently in a hospital in some cases. In those cases, even if picture quality is slightly deteriorated, a diagnosis can be often carried out sufficiently if an intermediate density portion appears. For example, it is sufficient that an X-ray film taken when an infant swallows a foreign matter by mistake can urgently specify the place of the foreign matter, and it is not necessary to wait for the heat-up until picture quality having high precision can be obtained. A thermal recording printer described in JP-A-7-125295 serves to carry out prediction such that a temperature reaches a predetermined temperature immediately before a sheet comes to a fixing section, thereby performing an estimated start, and persistently predicts a development enabling temperature. Therefore, only a time taken for the sheet to reach the fixing section can be saved and a considerable time cannot be saved in case of emergency described above.